Limits to What We Know
We Can’t Model What We Don’t Know
Modeling climate change is a far greater challenge than landing a man on the moon. Climate is a complex interdependent natural system than we still do not understand completely, and it interacts with our human-built systems in multiple ways that we can’t always anticipate. Climate scientists rely on computer modeling to capture the enormous number of variables that affect our climate and factor into the severity of impacts. These models have steadily become more sophisticated since the first report on climate change in 1990 from the Intergovernmental Panel on Climate Change (IPCC), and all have consistently predicted a rapid warming of the planet.
Nevertheless, climate models only include what scientists know today to be factors that affect global warming and its effects on climate. When new questions are raised, scientists seek answers and refine the models based on their findings, adding new layers to an already complex set of variables.
Consider Esieh Lake, which sits in Alaska above the Arctic Circle. It is one of eleven lakes studied by scientists in recent years because the lakes spew methane into the air from an unexpected geologic source. As reported in the Washington Post, the prevalence of such lakes can have a significant impact on climate change. The scientists who made this discovery recommended in their study, which appeared in the journal, Nature Communications, in August 2018, that climate models be updated to incorporate this new finding.
Similarly, research published in the journal Nature suggests that the Earth’s oceans are warming at a much faster rate than previously anticipated, absorbing as much as 60% more heat since the 1990s than was estimated in older studies. In interpreting the study for its audience, Scientific American noted that as the oceans warm, their ability to absorb carbon dioxide decreases. Because the oceans are warming at a faster rate, they are leaving more CO2 in the atmosphere than scientists had thought, meaning that current predictions of global warming are likely to underestimate the impacts of climate change.
The bottom line is that we can’t know what we don’t know. We can only continue to ask questions where there are gaps or limited data in our understanding, and then support the studies that will strive to answer them.
Clarifying How Much We Can Know
Predicting climate change involves many different kinds of outcomes involving many variables, both known and unknown. Not all predictions are made equally. For some, more evidence and more agreement within the scientific community leads to more confident predictions. This is why scientists involved with the work reported by the IPCC have been very careful to distinguish the different aspects of climate change by clarifying the likelihood of a particular conclusion and their confidence level in their predictions.
As explained in a fact sheet from the Australian government, the IPCC Fifth Assessment Report uses two terms, “confidence” and “likelihood”, to describe climate change predictions. Confidence levels are determined by a combination of evidence and the degree of scientific agreement; the confidence level of a conclusion describes how confident scientists are in that conclusion, based on the robustness of the evidence and degree of scientific agreement. Unlike findings that prompt the use of the confidence scale, the likelihood of an outcome, expressed as a percentage, is used for conclusions that are generated by hard, measurable data and for which statistical probability of occurrence can be calculated.
The charts below, copied from the fact sheet, explain the range of confidence and likelihood found in the report.
Defines the statistical probability of predicted outcomes
Defines the level of agreement relating to scientific evidence
Two examples illustrating the application of these scales from the IPCC 2014 Synthesis Report:
- “It is “very likely” that sea level will rise in more than about 95% of the ocean area.”
- The IPPC has high confidence that a “large fraction of species faces increased extinction risk due to climate change ….”
Tipping Point for Stopping Climate Change
Scientists do not know the point at which emissions of greenhouse gases will trigger abrupt climate changes that we will be unable to reverse. In the IPCC’s 2014 Synthesis Report, they asserted with medium confidence that “the risk associated with crossing such thresholds … increases with rising temperature”.
In 2018, a team of researchers suggested we might be getting closer to such a tipping point without identifying the exact point. They note that eliminating emissions of greenhouse gases may not be sufficient to stabilize global temperatures at a given point such as 2°C. Pointing out that the climate system has many feedback mechanisms, the researchers suggest that these mechanisms, which have already been triggered to some extent, may continue to warm the earth to a point beyond the 3°C rise that has so concerned scientists. The researchers agreed with the assessment of the IPCC 2014 report that allowing temperatures to continue to rise only brings us closer to the tipping point.